The present invention relates to combustion engines and, more particularly, to an engine incorporating a low mass, high-rate shock-absorbing cylinder head component which suppresses combustion knock caused by very high reaction rates.
There are strong demands for engines that exhibit the following characteristics and even combinations of the following characteristics: high power density using heavy distillate hydrocarbon fuels (diesel, JP-5, JP-8, etc.); multi-fuel capability; substantially reduced emissions of exhaust pollutants; reduced knock sensitivity; and high power density closed-cycle operation. The present invention relates to a newly-developed engine that is extremely fuel tolerant and capable of efficiently using any fuels ranging from 0 to 130 in octane value.
The new technology exhibited by the engine of the present invention effectively utilizes homogeneous charge compression ignition (HCCI) combustion, and is also well suited to spark ignited combustion and late-cycle injection diffusion combustion characteristic of diesel engines. HCCI combustion has long been considered a combustion phenomenon of great theoretical benefit, but very little practical substance. This unique type of hybrid combustion can, in theory, combine the best elements of diesel combustion with the best elements of spark-ignited combustion. The substantial problem affecting the useful utilization of HCCI combustion is the very high rate of energy release (severe detonation) resulting from the compression-ignition of a homogeneous charge.
Detonation produces very high instantaneous cylinder pressure and temperature that rapidly damages or destroys engine components. Spark ignited engines have controlled energy release rates (burn rates) which are governed by the rate of flame travel across the combustion chamber. Diesel cycle combustion rate is controlled by both mixing rate and fuel injection rate.
An important feature of the engine of the present invention is its ability to accommodate very high reaction rate combustion without subjecting the engine structure to the destructive stresses caused by excessively high cylinder pressures and temperatures which are typical of very high reaction rates. The homogeneous air/fuel mixture present for HCCI combustion is highly reactive when compression ignited and lacks control elements to limit the reaction rate. The present inventive engine incorporates a low-mass, high-rate, shock absorbing cylinder head component which suppresses combustion knock caused by very high reaction rates. This present inventive system effectively limits peak cylinder pressure and temperature, hence limiting structural and thermal loads imparted to the engine.
Traditionally, there have been two primary forms of reciprocating piston internal combustion engines: compression ignition (CI) and spark ignition (SI) engines. While these engine types have similar architecture and mechanical workings, each has distinct operating properties which are vastly different from each other.
Spark ignited engines, commonly called gasoline engines, use a spark plug to initiate the combustion event. Compression ignited engines, also called diesel engines, utilize the heat generated by the rapid compression of air, and the timed injection of fuel into the combustion chamber to initiate combustion.
Gasoline and diesel fuels have vastly different distillation and combustion characteristics, even though they have quite similar energy densities (btu per pound of fuel) and latent heat of vaporization values. Despite some similarities, the combustion of diesel fuel in a compression ignition engine is much different than the combustion of gasoline in a spark ignition engine.
There is substantial demand for engines with high power density (HP/pound of engine weight) that use heavy distillate fuel (diesel fuel, for example). Lightweight two-stroke cycle gasoline engines exhibit superb power density, but do not use heavy distillate fuel. A diesel engine which uses such heavy distillate fuel, has a low power density for two principal reasons:
(1) Weight. The diesel engine requires robust engine structures and components to accommodate the high loads imparted by diesel combustion. PA1 (2) Power Output. The diesel engine is speed-limited to 3000-5000 RPM. Horsepower is a function of both speed and torque. Additionally, diesel combustion at the maximum permissible exhaust smoke limit can typically only use 75% of the available oxygen in the air.
On the other hand, modern two-stroke gasoline engines exhibit very high power density, but are typically highly intolerant of heavy fuels. Attempting to operate a spark ignited gasoline engine on heavy fuel is very difficult. If the fuel is sufficiently heated (600.degree. F.) and properly dispensed into the intake air stream, the engine will run, provided the engine is run at an air/fuel ratio (A/F ratio) richer than or near a stoichiometric ideal. At such A/F ratio, the heavy distillate fuel is running in a spark ignited mode which is very different than the compression ignition of diesel cycle combustion. Within a few seconds of running, spark ignited, heavy fueled combustion becomes unstable and knocks or detonates. Engine failure may occur as quickly as 5-10 seconds after detonation occurs.
Past HCCI combustion research efforts have been guided and limited predominately by the narrow margins of acceptable operating regimes, i.e., operating regimes that allow the engine to run without knocking. This inability to control knock has severely limited the practical effectiveness of HCCI combustion. Therefore, realization of effective and practical HCCI combustion is possible if an engine is designed that is either detonation tolerant or detonation non-susceptible. The present invention provides such a practical HCCI design.
The engine of the present invention is appropriately designed to be tolerant of knock or non-susceptible to knock thereby achieving excellent operation by running in the HCCI combustion mode.